In recent years, the world has witnessed explosive growth in the demand for all types of communications and it is predicted that this demand will increase in the future. It is expected that power line carrier (PLC) will play a major role in providing communications in the home, SOHO and corporate enterprise environments. One of the main attractions of using PLC communications is that communications take place over existing electrical power utility wiring. Networks running over traditional LAN cabling require that copper or optical fiber cable be installed, usually at great labor and material expense. PLC networks, however, do not require any special installation of cable since they utilize the power line wiring that already exists in the building structure.
In addition, it is a growing trend within the electrical device industry to enable previously stand alone electrical devices, such as sensors and lighting control devices, to communicate with each other over some type of communications network. Previously, sensor, switch and control devices communicated using point-to-point connections. Nowadays, manufacturers are building communication means into these devices to enable them to communicate over some type of shared medium constructed as one or more local area networks (LANs). A variety of systems is currently commercially available which electrical device manufacturers can integrate into their products to enable them to communicate over a network. A convenient medium for these devices to communicate over is the power line since most devices are already coupled to the wiring system for drawing electrical power.
One such communication system is the CEBus system that has been made an EIA standard) known as the EIA 600 standard, which was originally developed by Intellon Corp. A second well-known communications system is the LonWorks system commercially available from and developed by Echelon Corp. Both the CEBus and LonWorks systems specify physical and link layer means for communicating over a variety of different media including power line carrier, coaxial cable, fiber optic cable, radio frequency (RF), infrared (IR) and twisted pair cable.
The commonly used ISO OSI communications model specifies a seven layer communications protocol stack comprising a physical layer, link or media access control (MAC) layer, network layer, transport layer, session layer, presentation layer and an application layer. The main functionally of the MAC layer and associated protocol, is to provide an effective method of accessing the physical channel, which in this case is the power line. Along with basic channel access, the MAC protocol ideally also provides (1) efficient and reliable host packet and session transport for the different kinds of possible connections, including unicast, multicast and broadcast, (2) efficient addressing scheme for the stations connected to the network, (3) repeater functionality for large networks with stations spread over large distances and (4) quality of service functionality.
The main function of any MAC protocol is to provide an effective channel access method that enables efficient and reliable host packet transport for the different kinds of possible connections, e.g., unicast, multicast and broadcast connections.
A channel access scheme that is in widespread use today is known as Carrier Sense Multiple Access (CSMA) that is used for example in Ethernet LANs (IEEE Standard 802.3). A more innovative scheme is the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) that is used in wireless LANs (IEEE Standard 802.11). Both are commonly used in networks that comprise shared media whereby multiple nodes simultaneously have access to the same media. The media may be any physical medium that can be simultaneously shared by many nodes, such as a cable, RF, powerline, etc.